<template>
  <div class="spec-preview">
    <img :src="imgObj.imgUrl" />
    <!-- 移动到后显示的放大效果 -->
    <div class="event" @mousemove="handler"></div>
    <!-- 移动到后显示大图 -->
    <div class="big">
      <img :src="imgObj.imgUrl" ref="big" />
    </div>
    <!-- 遮罩层 -->
    <div class="mask" ref="mask"></div>
  </div>
</template>

<script>
export default {
  name: "Zoom",
  props: ["skuImageList"],
  data() {
    return {
      currentIndex: 0,
    }
  },

// 计算属性只要用到的响应值发生变化，便会重新就重新计算
  computed: {
    imgObj() {
      return this.skuImageList[this.currentIndex] || {};
    },
  },
     mounted() {
     this.$bus.$on('getIndex',(index) => {
      console.log(index);
      this.currentIndex = index
     })
    },
    beforeDestroy() {
      this.$bus.$off('getIndex')
    },
    methods: {
      handler(event) {
        let mask = this.$refs.mask;
        // offsetX是鼠标到big盒子的左边距离,这里需要算和event盒子到big盒子的左边的距离
        let big = this.$refs.big;
        let  left  = event.offsetX - mask.offsetWidth / 2 
        let top = event.offsetY - mask.offsetHeight / 2
        // 约束范围
        if(left <= 0) {
          left = 0
        }
        if(left >= mask.offsetWidth) {
          left = mask.offsetWidth
        }
        if(top <= 0){
          top = 0
        }
        if(top >= mask.offsetHeight) {
          top = mask.offsetHeight
        }
        // 修改元素的left和top的属性值
        mask.style.left = left + 'px'
        mask.style.top = top + 'px'
        big.style.left = -2 * left + 'px'
        big.style.top = -2 * top + 'px' 
      }      
    }
  
};
</script>

<style lang="less">
.spec-preview {
  position: relative;
  width: 400px;
  height: 400px;
  border: 1px solid #ccc;

  img {
    width: 100%;
    height: 100%;
  }

  .event {
    width: 100%;
    height: 100%;
    position: absolute;
    top: 0;
    left: 0;
    z-index: 998;
  }

  .mask {
    width: 50%;
    height: 50%;
    background-color: rgba(0, 255, 0, 0.3);
    position: absolute;
    left: 0;
    top: 0;
    display: none;
  }

  .big {
    width: 100%;
    height: 100%;
    position: absolute;
    top: -1px;
    left: 100%;
    border: 1px solid #aaa;
    overflow: hidden;
    z-index: 998;
    display: none;
    background: white;

    img {
      width: 200%;
      max-width: 200%;
      height: 200%;
      position: absolute;
      left: 0;
      top: 0;
    }
  }

  .event:hover ~ .mask,
  .event:hover ~ .big {
    display: block;
  }
}
</style>